Pronunciation: (plak), [key]
1. a thin, flat plate or tablet of metal, porcelain, etc., intended for ornament, as on a wall, or set in a piece of furniture.
2. an inscribed commemorative tablet, usually of metal placed on a building, monument, or the like.
3. a platelike brooch or ornament, esp. one worn as the badge of an honorary order.
4. Anat., Pathol.a flat, often raised, patch on the skin or other organ, as on the inner lining of arterial walls in atherosclerosis.
5. Dentistry.a soft, sticky, whitish matlike film attached to tooth surfaces, formed largely by the growth of bacteria that colonize the teeth.
6. Bacteriol.a cleared region in a bacterial culture, resulting from lysis of bacteria by bacteriophages.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.